1. Field of the Invention
The present invention relates to a method for setting the trigger power of a transmitter diode for optical data transmission by means of a first transceiver unit and a second transceiver unit.
2. Description of the Related Technology
Data transmission via optical paths, for example in the infrared wavelength range, is applied preferably for short distances, for example for communication from mobile phones and notebooks to personal computers (PCs). Another application is for data exchange between printers and PCs. Transmission is standardized and takes place in most cases in systems operating in the infrared range on the basis of a so-called IrDa protocol (IrDa=Infrared Data Association). Since data transmission takes place bidirectionally, combined transmitter and receiver units, made from so-called transceiver circuits for operating the transmitter and receiver diodes, are used in such components. The transceiver circuits in turn consist of a receiver circuit, a transmitter circuit, also known as a driver circuit, and an interface circuit which regulates the data exchange between the processor and the transmission and receiver circuit. The transmitter diodes used for data transmission are controlled from the driver circuit that converts the digital input signal, supplied via the interface circuit from a processor for example, into a current pulse. Depending on the transmission power of the transmitter unit, characteristics of the transmission path and sensitivity of the receiver system, the communication distance for data transmission in the infrared range is between 30 cm and 3 meters at the most. Because of the requirement to also transmit visual information within a reasonable time, systems are now made with transfer rates of 4Mbit/s. Since with higher transfer rates the demands imposed on the transmission paths also rise sharply, it is possible within the scope of the IrDa protocol for example to reduce the data rates under unfavorable transmission conditions.
In the case of the known state-of-the-art methods, the transmitter diodes are controlled from the driver circuits with fixed current values. These can either not be varied by the user, such as the 115.2 kbit/s infrared transceiver HSDL 3201 from Hewlett Packard, or they can be selected by the user with a fixed value, as in the case of the IRMS6100 from Infineon, or they can be set by the user to a fixed value by means of an external resistor, as in the case of the TSLM1100 transceiver from Texas Instruments.
It is a disadvantage of the method operating in accordance with the known state of the art that the transmission power which is set once is determined by the system and cannot be varied by the user or alternatively only with great effort, for example by using external components. Since for many devices that are not dependent on supply networks, such as mobile phones or notebooks for example, the power consumption is a critical factor, the communication distance is frequently limited to values under 1 meter, for example, by reducing the trigger power by a fixed predetermined amount. In conjunction with the transmission of ever increasing data volumes, the power consumption also rises rapidly. Since the battery capacity of the mobile devices is very limited and the operating time in the case of notebooks and mobile phones in particular is a decisive factor, ways must be found to keep the power consumption low for infrared data transmission on the one hand, and on the other hand to achieve as large a communication distance as possible and at the same time to prevent a drop in the data rates in order to rapidly transfer even large data volumes.
The object of the present invention is to provide a method with which the trigger power of the transmitter diodes can be set according to the communication distance. A further object of the invention is to specify a circuit arrangement for performing the method and which can be manufactured simply and at low cost.
According to the present invention, this object is achieved by the trigger power of a transmitter diode, from which a test signal is output, being modified appropriately in a first transceiver unit until a response signal is received with the currently set trigger power and the trigger power from the first transceiver unit is stored.
The further object is achieved by virtue of a driver circuit for supplying a driver current to an electronic data transmission component with:
a switching device that in a first state connects a circuit junction point to a supply voltage and disconnects from a constant reference current, and in a second state disconnects the circuit junction point from the supply voltage and connects to the constant reference current;
a voltage-controlled resistor to the input of which the supply voltage is applied, from the output of which the driver current is delivered, and whose control input is connected to the circuit junction point; and
a voltage-controlled measuring shunt to the input of which the supply voltage is applied, from the output of which a measured current is delivered having a preset relationship to the driver current, and whose control input is connected to the circuit junction point, the measured current being coupled to the circuit junction point with a sign that is inverted in relation to the constant reference current.
Accordingly, the essence of the invention consists in modifying the trigger power of a transmitter diode from a first transceiver unit that outputs a test signal until such time as a response signal is received from a second transceiver unit with the currently set trigger power. When this is the case, the value of the trigger power is stored by the first transceiver unit. A following data transmission session is preferably performed with the trigger power value last stored.
Studies carried out by the applicant have shown that it is advantageous for the value of the set trigger power to be modified only when no response signal has been received within a time window that begins with the output of the test signal. A test signal with modified trigger power is then output in a subsequent time window.
In a further development of the method according to the invention, a check is made at the very beginning to determine whether data transmission is possible under the existing transmission conditions that prevail due to the system configuration. For this purpose, the test signal is output with the maximum trigger power during the first time window and, provided a response signal is received, the trigger power is reduced successively in subsequent time windows. It is an advantage compared with the known state of the art that with little additional time considerably less power is needed for data transmission.
In another further development of the method according to the invention, the test signal is output with minimum trigger power during a first time window and the trigger power is increased successively with each further time window until a response signal is received. If in addition the response signal is returned with maximum transmission power, the transmission characteristics of the return path can thus be blanked out.
In order to keep the power consumption low during the setting phase, it is advantageous to generate as test signal a signal that varies with time by triggering the transmitter diode with pulses that are as short as possible. In the case of a longer data transmission session or if data transmission is interrupted, it is also advantageous to repeat the setting of the trigger power by generating the test signal with the trigger power value last stored.
Studies carried out by the applicant have shown that it is advantageous for the modification of the trigger power when the current through the transmitter diode, referred to as driver current hereinafter, is varied by the driver circuit in the transceiver unit which comprises an interface circuit, a receiver circuit and a driver circuit.
For this purpose, the present new circuit arrangement can be used advantageously to implement the method according to the invention. It provides a driver circuit for supplying a driver current to an electronic data transmission component, such as a transmitter diode for example, with the following characteristics: a switching device which in a first state connects a circuit junction point to a supply voltage and disconnects from a reference current source, and in a second state disconnects the circuit junction point from the supply voltage source and connects to a constant reference current source; a voltage-driven resistor, the control input of which is connected to the circuit junction point; and a voltage-controlled measuring shunt to the input of which the supply voltage is applied and from the output of which a measuring current is supplied having a fixed relationship to the driver current and whose control input is connected to the circuit junction point, the measuring current being linked to the circuit junction point with a sign that is the inverse of that of the constant reference current.
The advantage of the driver circuit of the present invention compared with the state of the art is due to the fact that it permits the level of the current pulses to be set and a high data rate at high currents. Thus, for example, precise current pulses can be generated with settable or programmable current at a high data transfer rate of several Mbits. This settability makes it possible to utilize the minimum necessary current intensity for the actual transmission path in order on the one hand to cover long paths and on the other to minimize current consumption and thereby to extend the battery life. Furthermore, it is an advantage that the load can be connected to-ground.
In particular, this is achieved by a measuring transistor and an output transistor which are so connected that the output current flowing through the output transistor is a fixed multiple of the current flowing through the measuring transistor. The control inputs of the two transistors are joined at a common junction point which is discharged by the reference current and charged by the current which flows through the measuring transistor. In a steady-state condition, the output current is therefore regulated to a fixed multiple of the reference current.
In one example of embodiment, the driver circuit is used for an infrared transmitter diode for wireless communication in accordance with the IrDA standard, the driver circuit being in CMOS technology. MOS transistors are used as voltage-controlled measuring resistors, designed such that the current flowing through the voltage-controlled resistor is a fixed multiple of the current flowing through the voltage-controlled measuring resistor, the relationship between these two currents being settable by the ratio of the transistor widths of the two voltage-controlled resistors at the time of designing the circuit. In addition, the measured current is linked via two series-connected current mirrors to the circuit junction point that is connected to the control terminals of the two transistors so that voltage decoupling is achieved between the measuring transistor and the circuit junction point.
Whereas in the driver circuit described above the driver current is set by means of the reference current, alternatively several driver circuits according to the invention can be used in order additionally or alternatively to the varying of the supplied reference current to set the driver current by connecting or disconnecting the driver circuits whose outputs are connected together for addition of the currents and each of which supplies a fixed driver current. A circuit arrangement of this kind is advantageous because, due to the division of the driver stage into identical blocks, the making capacity and the speed depend largely on the technology and operating parameters and not on the current that has been set.
The advantages of the present invention are also due to the fact that, with the driver circuit according to the invention, regulated driver current can be generated faster and the driver current varies only slightly with changes in the supply voltage applied, and with temperature and technology variations.